The goal of this research program is to demonstrate a fiber-integrated, compact, high power, and electronically controlled femtosecond system at 780 nm, which is specifically designed for multiphoton endoscopic imaging for cancer detection and diagnostics. The research activities will explore the concept and devices for generating femtosecond pulses using active electro-optic phase modulation in a loop configuration. The proposed approach is dramatically different from the common mode-locking techniques and uses entirely linear optics, enabling adjustable pulse repetition rate and pulse width. The chirp of the output pulse can be electronically tuned to compensate the linear dispersion of several meters of optical fiber, allowing fiber delivery of femtosecond pulses without the cumbersome free-space grating pairs. Leveraging the highly mature and integrated techniques that have been developed for the telecommunications industry, the proposed research efforts will create "telecom grade" femtosecond sources that are truly robust and turn-key, and tailored specifically for in vivo endoscopic imaging. Such sources will be essential for the practical implementation of multiphoton endoscopy for cancer research, particularly to biomedical experts that are not trained in lasers and optics. The proposed research involves close collaboration between Cornell University (the PI and Co-PI Warren Zipfel) and electro-optic device innovator Dr. Suwat Thaniyavarn of EOSPACE Inc. (Redmond, WA.). The three specific aims are: 1. Design and fabricate an integrated electro-optical loop for spectrum generation. 2. Design and fabricate a fiber-integrated femtosecond system at 780 nm. 3. Demonstrate the significance of this new femtosecond source for multiphoton endoscopic imaging for cancer research. The industry-academia collaboration established by this program strongly couples biomedical imaging and the fiber-optic communication industry, creating great synergies between two seemly divergent fields and providing new opportunities for innovation in biomedical imaging.